1. Field of the Invention
The invention is concerned with the field of radar technology. In particular the invention relates to radar systems in which the irradiation or reception antenna is protected against weather influences by a front fitting.
2. Description of the Related Art
Radar systems with their ability to detect movement and determine distance and speed are operated in different fields of application. The antennas of the radar sensors are typically arranged directly behind a protective cover (radome). This cover can also be embodied as a lens of dielectric material for influencing the beam path (for example focussing) of the electromagnetic waves used. Contamination on this cover, for example due to dust, mud, ice, or sleet, can cause the propagation of signals to be impeded and thus adversely affect the detection power of the sensor.
Many applications, in particular those with a relevance for safety, have a certain minimum degree of sensor sensitivity and permanent and reliable monitoring to determine whether the sensitivity drops below these minimum values is necessary. To do this, standardized reflection objects (what are referred to as calibrators) can be used which are located in the capture range of the radar. A further possibility is to form statistics on the intensity and frequency of registered reflection signals and to infer changes in the sensitivity of the sensor from deviations. However, depending on the field of application, these methods are not practical and are too slow or too imprecise.
Thus, for example for applications in motor vehicles, not only comfort-related but also safety-related functions are being increasingly made available on the basis of radar sensor systems. Due o the specific environment and the installation position, it is particularly easy here for dirt, ice or snow on the radome to adversely affect the functional capability of the sensor.
In such a highly variable field of application with a number of sensed objects which varies in an irregular way, statistical methods are unsuitable, or at least problematic, for functional checking as both distances and speeds of the detected objects and their respective reflection characteristics may vary. Calibrators may be used basically only for stationary operating modes (as a defined target object at a predefined distance with known reflection properties), and can therefore not be used during mobile application.
In DE 196 44 164, a motor vehicle radar system is described in which a front fitting made of dielectric material is mounted in front of the antenna system, this front fitting having the function of a lens or of a radome. In order to detect soiling or a coating it is proposed to apply an electrically conductive arrangement made of two or more components which are electrically separated from one another on the external surface of the radome which is exposed to the weather. Changes in the electrical resistance and the capacitance between the separated components of the conductive arrangement which are brought about by adhering material (dust, ice, etc.) are measured arid ultimately enable conclusions to be drawn about the damping properties of the coating by way of the influence on what is referred to as the loss angle, which is calculated therefrom.
This device has various disadvantages:
Therefore the conductive arrangement, that is to say for example conductive tracks made of metal, is permanently exposed to weather influences. As, for functional reasons, the conductor tracks must not be insulated (resistance measurement), chemical factors (oxygen in the air, moisture, road gritting materials, etc.) and physical factors (UV radiation, stoning etc.) act intensively on the conductive arrangement. For this reason, as well as corrosion of the conductive material, it is also possible that the underlying dielectric surface may become detached or the conductor tracks may be mechanically damaged (stoning) and the arrangement suffer irreparable damage. In addition, the arrangement only supplies information relating to resistance values and capacitance values between conductor tracks which can be falsified by a large number of influences: a local electrically conductive bridge (insects, salt water spraying, soot particles, etc.) would, for example, be erroneously assigned to a distributed layer as a surface resistance.
An indirect calculation of damping properties of a coating on the basis of these measured variables is therefore associated with a relatively high degree of inaccuracy.
A drop in performance or failure in the radar system itself (for example due to a defect in the transmission/reception electronics) is not detected by the proposed arrangement. Additional measuring devices according to DE 196 44 164 are necessary for this.
The present invention is based on the prior art described in DE 196 444 164. The object of the present invention as to develop a new method and corresponding devices for improved monitoring of the power of a radar system which is equipped with a radome.
This object is achieved by means of a method for detecting a power-reducing coating (5) on a radome (2) of a radar system, said method comprising: feeding to a receiver of said radar system a monitor signal comprising a modified part of electromagnetic radiation emitted by said radar system and modified by interaction with said power-reducing coating and evaluating said monitor signal, whereby said power-reducing coating is detected, and by means of a device for detecting a power-reducing coating (5) on a radome (2) of a radar system, wherein said device comprises at least one element(3, 7, 9) for modifying part of the irradiated radar radiation and transmitting this part to a receiver device (4), each element (3, 7, 9) being arranged in such a way that the coating (5) present on the radome (2) influences the modified radiation. Further details and advantages of various refinements according to the invention emerge from the features of the subclaims.